I used the Mandalorian BP. What I did was measure my collar bones (where I felt the collar piece would go) and also the collar blueprint. Then I used ratios to scale the prints down to something that would look proportioned correctly.
It should look like:
your size (a) x
--------------- = -------
actual size (b) 100
(sorry, the post takes out the spaces, but hopefully you'll get the idea)
then multiply your size (a) by 100 and actual size (b) by x.
For example, if your size is 14 inches, then you'd have 1400=(b)x (I forget what the actual size is.)
Then divide both sides by (b) so that x is alone. That will be your ratio. So you should multiply all measurements on the plans by that number, and it should look great.
I've seen people with armor too big (small people) and armor too small (big people) and adjusting the size to you always is better than just going with what's out there.